The present invention relates to a fabrication method of Ge—Mn magnetic semiconductor by adding a transient metal Mn into a Group IV semiconductor Ge. More particularly, the invention relates to a fabrication method of Ge—Mn magnetic semiconductor with a high Curie temperature by converting the microstructure of the magnetic semiconductor into an amorphous structure and adding a large amount of Mn solid solution.
As Moore's law vindicates, the electronic devices including semiconductor IC have been undergoing a continuous cycle of progressive development. As a result, the electronic device development is considered to be getting closer to the technological limit. Many types of technologies have to be considered for fundamentally resolving this problem and the next generation spin electronic device technology is one of the strong candidates which is attracting a significant attention at present.
The essence of the spin electronic device technology is simultaneously utilizing the characters such as charge and spin from the classical dynamics and quantum mechanics, respectively. The present electronics technology only employs the charge character from the classical dynamics. Hence, in order to fabricate a spin electronic device, in addition to the technology for controlling the charge of an electron in semiconductor, the technology to control the spin of an electron is also necessary.
The spin electronic control technology encompasses the techniques of spin injection, transfer and detection. The spin injection is especially important among these techniques. The reason is that the length of spin coherence is on the order of a few hundred μm and the techniques of either electrically or optically detecting spin are relatively well established.
The method which was first proposed for injecting spin into a semiconductor is utilizing ferromagnetic materials. More specifically, ferromagnetic material/semiconductor hybrid structures are used. While electrons are passing through the hybrid structure of a ferromagnetic material, a polarization occurs. Then, this polarized spin is injected into the semiconductor.
Ferromagnetic materials include transition metals such as iron, cobalt, nickel or their alloys. The spin polarization rate of the transition metals and their alloys is around 50%. The hybrid structure for injecting spin is a relatively simple one. Since the Curie temperatures of ferromagnetic transition metals are mostly higher than room temperature, it is advantageous for the perspective of commercial development of spin electronic devices.
However, the spin injection rate so far obtained from the hybrid structure of these ferromagnetic metals/semiconductors is much lower than expected. At the beginning, the inferior results were interpreted as occurring from an improper control of the surface characteristics. However, more recently, it was thought to be caused by more fundamental phenomena such as a mismatch of energy band structure between the metals and semiconductors.
A magnetic semiconductor is one of methods that have been developed to tackle this problem. More specifically, the magnetic semiconductor is utilized instead of a ferromagnetic metal in the metal/semiconductor hybrid structure. At present, two types of magnetic semiconductors are actively being researched. One of them is magnetic semiconductor from group II-VI and the other is from group III-V.
The magnetic semiconductors from group II-VI have a spin polarization efficiency of almost 100%. They also have very good spin injection properties. However, their Curie temperatures are so low that they can only be obtained at liquid helium temperature and the good spin injection properties are obtained under the influence of a strong magnetic field.
In comparison, the recently developed magnetic semiconductors from group III-V have much higher Curie temperatures than those from group II-VI. However, their Curie temperatures are still below room temperature. This is a major stumbling block to their commercial development. As a result, one of the most important issues in the development of magnetic semiconductor is raising the Curie temperature.
To date, most of researches in magnetic semiconductors are constrained to the magnetic semiconductors from group II-VI and group III-V. However, a new range that was added recently is the semiconductors from group IV. Especially, Ge based semiconductors are attracting a significantly attention. Like the magnetic semiconductors from group III-V, the ferromagnetic property is imparted to Ge by adding 3d transition metals to Ge. Most representative transition metal is Mn.
However, the solid solubility of Ge and Mn are very low hence causing difficulty in making a large amount of Mn solid solution. Also, this is a major problem for raising the Curie temperature. In order to resolve this problem, a low temperature. MBE method has been utilized. Y. D. Park et al., disclosed the method of making an Mn solid solution of 3.5 atomic % in Ge using the low temperature MBE method (“A Group IV ferromagnetic semiconductor: MnxGe1-x”, Science 295, pp. 651-654 (2202)). At this instance, the Curie temperature is 116 K which is much lower than room temperature. This may be due to insufficient amount of Mn.